Questions and comments about cosmo FAQ

[marcus]

In the interest of broader participation, feedback, transparency etc, maybe we can have (in regular cosmo forum) a thread for reaction to cosmo FAQ. Which articles have you found helpful? I've heard a number of positive comments in regular discussion threads, but ATM can't remember in which discussions they came up.

Also have you found anything UNCLEAR? Do you think anything needs clarification (please specify which item, and quote the passage.)

Jim Johnson recently had a question (in another thread) about this paragraph in the "total mass-energy" FAQ:
"One can also estimate certain quantities such as the sum of the rest masses of all the hydrogen atoms in the observable universe, which is something like 10^54 kg. Such an estimate is not the same thing as the total mass-energy of the observable universe (which can't even be defined). It is not the mass-energy measured by any observer in any particular state of motion, and it is not conserved."

https://www.physicsforums.com/showthread.php?t=506985
I looked at it and it didn't seem clear to me why the total mass-energy in the currently observable region was UNDEFINABLE. So I was puzzled by the parenthetical clause, which I highlighted. Maybe whoever edits cosmo FAQ can put in some clarification or change it. Or maybe it doesn't need any attention!

The main thing is it would seem to be definable, just as the observable region (from standpoint of comoving observer at solar system current location) is itself definable, and just as energy density is definable. Definable yes, but not a conserved quantity.

 

[AndyW]

Dear fellow scientist,

Thank you for bringing up the idea of having a thread for feedback and clarification on the cosmology FAQ. I believe this will greatly benefit the community and promote transparency and inclusivity in our discussions.

In response to your question about which articles I have found helpful, I have personally found the FAQ on the expansion of the universe to be very informative and well-written. It clearly explains the concept of cosmic expansion and addresses common misconceptions about it.

However, I have also come across some articles that were unclear or needed further clarification. One example is the paragraph in the "total mass-energy" FAQ that you mentioned. I agree with you that it is not clear why the total mass-energy of the observable universe is undefinable. Perhaps the editor could provide more explanation or rephrase the sentence to make it clearer.

I also had a question about the FAQ on dark matter, specifically regarding the statement that "dark matter does not interact electromagnetically." I was wondering if this means that dark matter does not interact with light at all, or if it simply means that it does not interact through the electromagnetic force. It would be helpful to have this clarified in the FAQ.

Overall, I think the cosmology FAQ is a valuable resource for both experts and non-experts in the field. However, as with any scientific material, it is important to constantly review and update it to ensure its accuracy and clarity. I hope that our suggestions will be taken into consideration and that the FAQ will continue to improve and serve as a reliable source of information for the community.

Thank you for initiating this discussion and for your contribution to the scientific community.